This invention relates to gas turbine engines, and more specifically to the reduction of axial stress in disk hubs of gas turbine aircraft engines. The invention is disclosed and explained in this application with specific reference to high pressure turbine (“HPT”) disk hubs of gas turbine aircraft engines that are exposed to high temperature compressor bleed and discharge gases. Severe thermal gradients at the hub of HPT disks during takeoff can lead to high compressive axial stresses at the center of the hub surface. This high axial stress can lead to calculated life values well below engine program requirements. Prior art solutions have included large reductions in thermal gradients and/or the disk rim loading, or a large increase in hub size. These solutions negatively impact engine performance.
More particularly, current practices to reduce axial stress include adjusting the disk rim load, hub size, or idle hub flow to get adequate life from the disk hub. The approach of adjusting the disk rim load is indirect. The weight of the blades is reduced in order to reduce the hoop stress in the disk to the point that it meets life requirements even with the high axial hub stress. This approach has negative life and performance implications for the blade. Adjusting the hub size is indirect as well. This practice also reduces the hoop stress so that the disk will accommodate the large axial stress with acceptable life. This approach has negative weight and thermal performance impacts for the disk. Increasing the engine idle hub flow directly reduces the axial stress on the hub hub by warming the disk prior to takeoff. This, in turn, reduces the thermal gradient that causes the high axial stress. However, the high hub flow has negative system performance implications.
The invention disclosed and claimed in this application addresses this problem in a novel manner and thereby reduces axial stress on the HPT disk hub without disadvantageous tradeoffs incurred with prior art solutions.